Work around missing _Exit in old API levels.

Rather than do this in libandroid_support, we may as well just stick it with
the other historical stdlib workarounds in bionic itself...

Bug: N/A
Test: built new NDK test
Change-Id: Ia5cf4010581eb79d4adf924e87d0bc050b9e2839
diff --git a/libc/include/android/legacy_stdlib_inlines.h b/libc/include/android/legacy_stdlib_inlines.h
index e211de5..82186c7 100644
--- a/libc/include/android/legacy_stdlib_inlines.h
+++ b/libc/include/android/legacy_stdlib_inlines.h
@@ -36,6 +36,8 @@
 
 __BEGIN_DECLS
 
+__noreturn void _Exit(int) __RENAME(_exit);
+
 static __inline float strtof(const char *nptr, char **endptr) {
   return (float)strtod(nptr, endptr);
 }